A very large data store system may contain data that is stored on a plurality of separate disk drives. Such disk drives are sometimes referred to as back end data storage. Client applications may read and write the data in the data store systems, and the data store systems may map these access requests to the appropriate data stores. It may be desirable to replace or add one or more additional data stores and redistribute or migrate some of the data entries from legacy data stores to the one or more additional or new data stores. The added new data store systems may have desirable new technology to better and more efficiently serve client applications. Sometimes data stores may be decommissioned and/or removed from service as the device exceeds an expected service life or as the device begins to experience failures. In case of data store decommissioning or removal, the data entries on the subject data store may desirably be migrated to other data stores.